Structural Concrete Design: Load Differences and Limit States - MIT

This report provides a detailed explanation of the differences between dead loads, imposed live loads, and earthquake loads in the context of structural concrete design. It further elaborates on the key distinctions between the Ultimate Limit State (ULS) and Serviceability Limit State (SLS), highlighting their respective design considerations for safety, stability, usability, and comfort. The report also includes column checks related to bracing in a reinforced concrete structure, referencing relevant industry standards such as IS 875 and IS 1893-2014. It considers a building design located near the Wairarapa fault and determines the ULS seismic actions using the equivalent static method of NZS 1170.5.

DESIGN OF STRUCTURAL CONCRETE
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Difference between dead loads, imposed load live loads and earthquake loads
Dead loads define permanents or otherwise stationery loads that may be transferred to a structure
all through the lifespan and are often mainly as a result of the self-weight of the structural
members, weight of different materials, permanent partition walls as well as the weight of
permanent members. It is majorly composed of the weight of the columns, beams, walls, roofs
among others that were permanent aspects of a building. The dead load of every member is
determined by the volume of each of the section as a product of the unit load.
Imposed loads
Imposed loads are another category of vertical loads as considered in the design of structural
members. These refer to moving or movable loads that do not have an acceleration or effect.
Live loads are assumed to meant use or occupation of building inclusive of the weights of the
movable furniture, equipment, and partitions among others (Ghali, Favre and Elbadry, 2018).
There is a continuous change of live loads continuously. The loads are adequately assumed by
designer and form one of the major loads of design. The minimum live load values to be
assumed are provided in IS 875 which is a factor of the intended building use.
The code provided uniformly distributed load alongside concentrated loads. The design of the
floor slab has to be done in such a way it can carry concentrated loads or uniformly distributed
loads whichever generates more stresses in the part of the member that is under concern. As it is
barely possible that at any single point all the floors will not carry maximum loading
simultaneously, the code allows certain reduction in the imposed loads during the design of
foundations, load bearing walls, pier supports as well as columns.

Earthquake loads
Forces of the earthquake make up both horizontal as well as vertical forces on the structure. The
cumulative vibration as result of earthquake could be resolved in three perpendicular directions
that are mutual to one another, normally treated as horizontal and vertical directions. The
movement in the vertical direction do not result in superstructure to an important degree.
Nevertheless, horizontal displacement of the structure during earthquake has to be taken into
conisation at the time of design.
The nature of the soil, construction mode, size of the constructions well as the duration alongside
intensity of the motion of the ground are among the factors that affect the structure response to
ground vibration. The details of such calculations are given in IS 1893-2014 for the structures on
soils that would not significantly slide or settle appreciably as a result of earthquake.
The seismic acceleration for design could be attained from seismic coefficient that refers to the
ration of acceleration as a result of earthquake as well as due acceleration resulting from gravity.

For the case of monolithic reinforced concrete structures that are in seismic zone 2 as well as 3
that do not have 5 stories high as well as importance factor below 2, the seismic forces tend to be
important consideration in design.
Differences between the ULS (Ultimate Limit State) and SLS (serviceability limit state)
Ultimate limit state
The ultimate limit state defines the design for structure as well as users safety through limiting
the stress experienced by the materials. Ultimate limit state has to be attained as established
condition to abide by the engineering specification of stability as well as strength under various
design loads. The ultimate limit state is an entirely elastic conditions often situated in the upper
parts of the elastic zone. This is contrary to ultimate state that includes deformations tending to
collapse of structure and is situated deep inside the plastic zone (Taranath, 2016). Suppose all
factored bending, tensile or compressive as well as shear stresses are less than the determined
resistance then a structure would be declared satisfactory to ultimate limit state criterion, Safety
as well as reliability may be assumed so long as the criterion is attained as behavior of the
structure would be similar as under repetitive loadings.
Serviceability limit state defines designing to ascertain the usability and comfort of a structure.
This is inclusive of the deflections as well as vibrations alongside durability and cracking. Such
are the conditions which are not based on strength even though may declare the structure not
suitable for the intended use for instance it may result in discomfort of the occupants under
routine circumstances. It may as well include limits to non-structural issues including heat and
acoustics transmission. The requirement of serviceability limit state is relatively less rigid as
compared to strength-based limit states since structure safety is not considered (Grunewald,

Ferrara and Dehn, 2016). A structure thus has to remain functional for the intended use factor to
routine loading to attain serviceability limit state criterion.
Question 3
Column checks
The columns which are to be checked refer to those linked to bracings directly. There are a total
of 3 columns checked:
One linked to eccentric bracing at ground floor
One linked to eccentric bracing at first floor-X-direction
One linked to eccentric bracing at first floor-Y-direction (Moehle, 2015)
Columns with axial forces should attain condition:
Checking column resistance in the X-direction ground floor

References
Ghali, A., Favre, R. and Elbadry, M., 2018. Concrete structures: Stresses and deformations:
Analysis and design for serviceability. CRC Press
Grünewald, S., Ferrara, L. and Dehn, F., 2016. Flowable fibre-reinforced concrete: Progress in
understanding and development of design standards. In Proceedings 8th International RILEM
Symposium on Self-Compacting Concrete. RILEM publications SARL
Moehle, J.P., 2015. Seismic design of reinforced concrete buildings (pp. 230-235). New York:
McGraw-Hill Education
Taranath, B.S., 2016. Structural analysis and design of tall buildings: Steel and composite
construction. CRC press